libprojectM Release 4.1.1

This is a small bug fix release that corrects some issues found in version 4.1.

Changes since 4.1.0

Enhancements

• Added CMake USE_PTHREADS option for emscripten builds

Bugs

• Fixed a bug that prevented a preset's composite shader from being loaded if the warp shader was empty
• Fixes to GLM CMake targets/usage
• Fixed a broken #ifdef in the SDL test UI
• Fixed SOIL2 include directories